1. Field of the Invention
The present disclosure relates to liquid ejection heads that eject a liquid such as ink.
2. Description of the Related Art
As examples of ink ejection methods, a thermal method and a piezoelectric method are known.
A thermal method recording head includes a recording element substrate that has liquid chambers and heating elements. Nozzles through which ink is ejected are formed in the liquid chambers. The heating elements serve as energy generating elements. Application of heat by the heating elements to the ink supplied into the liquid chambers causes the ink to boil. Forces caused by bubble generation due to the boiling cause the ink to be ejected through the nozzles.
A piezoelectric method recording head includes a recording element substrate that has liquid chambers and piezoelectric elements. Nozzles through which ink is ejected are formed in the liquid chambers. The piezoelectric elements serve as energy generating elements. The piezoelectric elements are deformed when electrical energy is applied thereto. Due to deformation of the piezoelectric elements, ejection energy is applied to the ink supplied into the liquid chambers, thereby ejecting the ink through the nozzles.
Furthermore, nowadays a recording head is proposed that has a larger width than the width of a recording medium and that includes a plurality of energy generating elements arranged in the width direction of the recording medium (hereafter, simply referred to as “width direction”). Such a recording head is also referred to as a line-type head. With a recording apparatus equipped with a line-type head, an image can be recorded on a recording medium while conveying the recording medium in a direction that intersects the width direction (hereafter, referred to as “conveying direction”) without performing a scan with the line-type head in the width direction. This allows printing to be performed at a comparatively high speed.
In the case where a belt-shaped image that extends in the conveying direction is recorded on a recording medium by using the line-type head, out of the plurality of energy generating elements arranged in the width direction, some of the energy generating elements are continuously operated. When some of the plurality of energy generating elements are operated, the temperature is increased in portions of the recording element substrates, the portions being located near the continuously operated energy generating elements (hereafter, these portions are referred to as “continuous operation portions”).
For example, in a line-type head, to which the thermal method is adopted as the ejection method, part of heat generated due to the operation of the heating elements is transferred to the recording element substrate. As a result, the temperature is increased in portions near the continuously operated heating elements of the recording element substrate. In a line-type head, to which the piezoelectric method is adopted as the ejection method, part of electrical energy applied to the piezoelectric elements is converted into heat energy. As a result, the temperature is increased in portions of the recording element substrate, the portions being located near the piezoelectric elements, to which electrical energy is continuously applied.
In the recording element substrate, the temperature does not increase in portions near the energy generating elements that are not continuously operated (hereafter, referred to as “non-continuous operation portions”). Furthermore, a plurality of nozzles and a plurality of liquid chambers are formed in the recording element substrate. Thus, heat is not comparatively easily transferred within the recording element substrate. For this reason, heat is not easily transferred from the continuous operation portions to the non-continuous operation portions, and accordingly, the temperature distribution over the recording element substrate becomes non-uniform. Thus, the following problem tends to occur.
That is, ink supplied to the continuous operation portions of the recording element substrate is subjected to heat applied from the continuous operation portions, thereby the temperature of the ink is increased. Accordingly, the viscosity of the ink is increased. In contrast, the temperature of the ink supplied to the non-continuous operation portions of the recording element substrate is not increased, and accordingly, the viscosity of the ink is not increased.
It is known that the viscosity of the ink affects the amount of ink to be ejected, thereby affecting the print density of an image to be recorded. When the difference in temperature between the continuous operation portions and the non-continuous operation portions is large, the ink ejection amount from the continuous operation portions becomes different from that from the non-continuous operation portions, and accordingly, causing the ink ejection amount to vary in the width direction. This causes uneven print density in the recorded image, and accordingly, the quality of the image is degraded.
In particular, nowadays the demand for high-quality image for commercial use has been increasing in addition to the demand for high-speed printing performance with line-type heads. Accordingly, recording heads that reduce non-uniform temperature distributions over recording element substrates have been proposed (for example, Japanese Patent Laid-Open No. 2007-8123).
A recording element substrate of a recording head disclosed in Japanese Patent Laid-Open No. 2007-8123 has temperature adjustment flow passages through which a temperature adjustment solvent flows. The temperature adjustment flow passages extend in a direction in which a plurality of energy generating elements are arranged. In the recording head, by the solvent that flows through the temperature adjustment flow passages of the recording element substrate, continuous operation portions of the recording element substrate are cooled and non-continuous operation portions of the recording element substrate are heated. As a result, non-uniformity of the temperature distribution over the recording element substrate is reduced.
However, with the recording head disclosed in Japanese Patent Laid-Open No. 2007-8123, a pump that causes the solvent to flow and a solvent temperature controller that controls the temperature of the solvent are needed. Furthermore, power to operate the pump and the solvent temperature controller is also needed.
Japanese Patent Laid-Open No. 2009-149057 discloses a recording head that reduces non-uniformity of the temperature distribution over a recording element substrate without using a pump or a solvent temperature controller. The recording head disclosed in Japanese Patent Laid-Open No. 2009-149057 includes a support substrate serving as a support member that supports, out of surfaces of the recording element substrate, a surface in a nozzle array direction in which a plurality of nozzles are arranged. An ink flow passages, which communicate with liquid chambers of the recording element substrate, penetrate through the support substrate.
The support substrate does not have holes or grooves other than the ink flow passages, which communicate with the liquid chambers of the recording element substrate. Thus, heat is comparatively easily transferred within each support substrate. That is, the support substrate has the function of equalizing the temperature distribution with respect to the nozzle array direction over the recording element substrate. More specifically, heat of the continuous operation portions of the recording element substrate is transferred to the non-continuous operation portions of the recording element substrate through the support substrate. This suppresses an increase in temperature in the continuous operation portions and facilitates an increase in temperature in the non-continuous operation portions, thereby reducing non-uniformity of the temperature distribution over the recording element substrate.
However, in the recording head disclosed in Japanese Patent Laid-Open No. 2009-149057, heat of the support substrate may be transferred to the ink that flows through the ink flow passages of the support substrate. When heat is transferred from the support substrate to the ink, the heat of the continuous operation portions of the recording element substrate is not sufficiently transferred to the non-continuous operation portions of the recording element substrate through the support substrate. As a result, the temperature is not sufficiently increased in the non-continuous operation portions. This increases non-uniformity of the temperature distribution over the recording element substrate, and accordingly, degrades the quality of an image to be recorded.